DISK NOISE OF QUADRILAYER MNBI MAGNETOOPTICAL DISKS

Disk noise of quadrilayer MnBi magneto-optical disks with grooved glass substrates was investigated. Both reflectivity noise and polarization noise of MnBi disks were 20 dB higher than those of TbFeCo disks. The degree of c-axis orientation of a hexagonal MnBi layer, which is inversely proportional to fluctuation in the magnetization direction, and Mn oxide in a MnBi layer are not dominant origins of the high disk noise. Bi layers 20 nm in thickness on grooved substrates have many hillocks over 50 nm in height at land edges. Noise reduction of 10 dB can be achieved by using a flat glass substrate. Surface roughness on the Bi layers is one of the main causes of high disk noise of MnBi disks.